Hi Carl,
You must have misread my comments.
> Blown filaments are absolutely possible due to an internal tube failure.
> Consider the failure a parasitic, gas, lousy assembly, etc. Any one of
> those can do it.
Parasitics are not a cause of blown filaments, but mechanical
construction sure is...as is mechanical shock.
My opinion is people who blame all these amplifier failures on
parasitic are looking for a single explaination for multiple causes.
It makes them look like they "know all the answers" because they can
give an answer point blank no matter what the problem.
No one can disprove the answer without long technical explainations
that go beyond the grasp of most neophytes, so they feel relatively
safe with the tall tale of parasitics.
> A case in point is the huge number of Svetlana 572B's with blown filament
> failures....I had a least 2 dozen happen to me and my customers. Put them
> in a known stable amp such as a SB-200, turn it on and everything looked
> fine. Key the relay with NO DRIVE and "Bang". Svetlana has acknowledged
> the stability problem and has redesigned the tube. It was an acknowledged
> parasitic problem based upon internal geometry, not gas or poor
> construction.
I have a pile of Sevtlana 572B's here and they FAIL HV breakdown
tests. Almost 25 % arc at just over 3000 volts anode voltage.
The peak anode operating voltage easily exceeds 4 kV in the SB-200.
You must have talked to a real expert, since Svetlata employs off the
street sales people with little or no vacuuum tube experience. Of
course, you might have called Russia and talked to a real engineer.
Anyway, put a typical older Svetlana 572 in a SB-200, and
it's Russian roulette.
> I feel that Tom's response is irresponsible and is strictly a
> MFJ/Ameritron CYA smoke screen.
That's bunk and you know it. People fall back on personal attacks (in
particular you and a certain AG6) when they run out of technical
facts. If you can't impeach the data, attack the person responding as
dishonst.
> My congratulations to Svetlana for not only quickly responding to the
> problem but also admitting the reason. Eimac, etc could learn a lesson
> about customer relations.
Maybe instead of a personal editorial, you could explain to everyone
HOW a parasitic causes a filament to open and roll around in the
bottom of the tube.
I turned on my reading lamp last night. The filament popped. Was that
a parasitic?
73 Tom
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